Field of the Invention
The present invention relates to camera apparatus.
Recent research on photoelectric conversion devices and particularly solid state camera apparatus have been positively carried out in conjunction with the progress of semiconductor techniques, and the results of the research begin to be partially put to practical use.
These solid state camera apparatus are classified briefly into two types, the CCD and the MOS types. The CCD type camera apparatus employs the principle that potential wells formed under MOS capacitor electrodes of the apparatus store electric charges produced by incident rays, and, to read the charges, these wells are shifted sequentially with pulses applied to the electrodes, thereby transferring the stored charges to the output amplifier. There are some CCD type camera apparatus which each employ a pn junction diode structure as a light reception section and a CCD structure as a transfer section. On the other hand, the MOS type camera apparatus utilizes the principle that each of the pn junction photodiodes constituting the light reception section stores electric charges produced due to incident rays and, when the charges are read, the MOS switching transistors connected to the respective photodiodes are sequentially turned on, so that the stored charges are read out to the output amplifier.
The CCD type camera apparatus has a relatively simple structure. It also is subject to relatively low noise because only the capacitance of each of the electric charge sensors each including floating diffusion at the last stage of the apparatus contributes to the generation of random noise in terms of possible noise, thereby allowing photography at low illumination. Since, however, the restrictions on the process of forming the CCD type cameras cause a MOS type amplifier (provided as the output amplifier) to be disposed on a chip, a 1/f image noise which would be very noticeable in the image will be produced from the interface between the silicon substrate and the SiO.sub.2 film thereon. Thus although the noise is at a low level, the performance of the CCD type camera apparatus is limited. If a camera having a high density of cells is produced by increasing the number of cells used to attain high resolution, the maximum quantity of electric charges which can be stored in a single well decreases and the desired dynamic range cannot be obtained, which would be a big problem in providing high resolution solid state camera apparatus in future. Since, in the CCD type camera apparatus, the stored charges are transferred while the respective potential wells are shifted sequentially, even the presence of only a single defective cell would stop or worsen the charge transfer extremely, thereby lowering the yield.
The MOS type camera apparatus is slightly more complicated in structure than the CCD type camera apparatus, especially, that of the frame transfer type. However, the former is superior to the latter in that the former can be constructed so as to have a larger storage capacitance and a larger dynamic range than the latter. In addition, although one of the cells be defective, it does not affect other cells adversely because the former employs the X-Y address system. Thus the former is more advantageous in yield than the latter. However, the MOS type camera apparatus has several faults: an extremely large signal voltage drop and hence an output voltage drop because of the connection of each photodiode to the corresponding wiring capacitance on signal reading; occurrence of large random noises because of the presence of large wiring capacitances; picking up of fixed pattern noise due to different inherent capacitances of the photodiodes and horizontal scan MOS switching transistors, and more-difficult low illumination photography compared with the CCD type apparatus.
In future high resolution camera apparatus, the size of each of the cells will be miniaturized and the quantity of stored charges will be decreased. However, the wiring capacitance determined by the chip size will not change significantly although the width of each wire is decreased. Thus the MOS type apparatus will become more and more disadvantageous in S/N ratio.
Although the CCD and MOS type camera apparatus have the above advantages and disadvantages, they are gradually approaching a level of practical use. However, it can be said that they suffer from the a following essential problem encountered in developing high resolution camera apparatus required in the future.
In connection with these solid state camera apparatus, new systems have been proposed in Japanese Unexamined Patent Publications (Kokai) Nos. 150878/1981 157073/1981 and 165473/1981 which are each entitled "Handotai Satuzo Sochi" (Semiconductor Camera Apparatus). As described above, the CCD and MOS type camera apparatus each store at their main electrodes (for example, the source of a MOS transistor) electric charges produced due to incident rays. In contrast, the systems proposed by the above published applications are based on a new concept, that the electric charges produced due to incident rays are stored at their control electrodes [for example, the base of a bipolar transistor or the gate of a SIT (static induction transistor) or a MOS transistor] and that the electric charges produced by light rays control a flow of current. That is, while the CCD and MOS types serve to read the stored electric charges outside thereof, the systems proposed in those published applications amplify the stored electric charges using the amplification function of each cell and then read the amplified charges. In other words, the latter reads the charges as a low-impedance output by impedance transformation. Thus the systems proposed in the latter have several advantages: high output, wide dynamic range, low noise and non-destructive reading due to the fact that the carriers (electric charges) excited by light signals are stored at the control electrodes thereof. In addition, they each have a probability of attaining high resolution in future.
However, these each employ the X-Y address system basically, and each include a basic element structure which comprises the composite of each of the cells of the conventional MOS type camera apparatus and an amplifying element such as a bipolar transistor or a SIT. Thus they each have a relatively complicated structure. In addition, although they each have a probability of attaining high resolution, there are limits to their resolution as they are.
The non-destructive reading characteristic of these sensors has been used only to hold the photographied image signal a relative short period of time compared to what is possible.